1. Field of the Invention
The present invention relates to a wideband antenna, and more particularly, to a wideband antenna capable of achieving multiband or wideband operations, having good matching effect and adjustability, and reducing a required antenna size.
2. Description of the Prior Art
An antenna is utilized for transmitting or receiving radio frequency waves in order to communicate or exchange wireless signals. An electronic product with wireless communication functionality, such as a laptop and a personal digital assistant (PDA), usually accesses a wireless network through a built-in antenna. Therefore, to facilitate access to the wireless communication network, an ideal antenna should have a wide bandwidth and a small size to meet the trends of compact electronic products within a permissible range, so as to integrate the antenna into a portable wireless communication equipment. In addition, as wireless communication technology evolves, operating bands of wireless communication systems become various. Therefore, an ideal antenna should cover various frequency bands.
Nowadays, the most common antennas of wireless communication include various types such as inverted-F antenna, loop antenna, couple antenna, etc. The inverted-F antenna, as its name implies, has a shape similar to a rotated and inverted character “F”. Nevertheless, performances of the inverted-F antenna in terms of bandwidth and bandwidth efficiency are not good, especially in low-frequency bands. Therefore, additional metal segments are usually supplemented in its vertical direction. Consequently, the cost will be increased. Since the resonating length of a loop antenna, theoretically, needs to be one half of the wavelength, and the operating bands of the loop antenna are too narrow, loop antennas are unlikely to be applied to wideband applications. The couple antenna utilizes the coupling effect between components to resonate the required frequency band. However, the frequency bands are not easy to be adjusted.
Therefore, how to increase antenna bandwidths to meet wideband requirements of wireless communication systems with, such as long term evolution (LTE) systems, is an ultimate goal in this technical field.